Why did not Alauddin Khalji annex the Deccan kingdoms after conquering them?

Alauddin Khalji did not annex the Deccan kingdoms after conquering them because of the following reasons:

1. He realised that it would be practically difficult to control these distant lands from Delhi.
2. He was more interested in acquiring the wealth of these Deccan kingdoms for the maintenance of his huge army. The rulers of Deccan were forced to accept the overlordship of Allauddin Khalji and had to pay annual tribute to him.